The invention described herein was made in the course of, or under a contract with the U.S. Atomic Energy Commission.
Rockbolts have long been employed to strengthen or stabilize coal or other mine roof structures by tying together laminated or fissured rock strata. In the past, a rockbolt typically would consist of a steel rod of sufficient length to extend from the roof-line up into a region of relatively strong rock, perhaps 3 to 10 feet into the roof. An expansion wedge anchor at the upper end of the bolt is secured in the surrounding rock by rotating the bolt at the roof-line using a torque wrench to set the anchor and tension the bolt. A steel plate washer between the bolt head and the rock roof may be employed to spread the load to the rock.
In order to improve the contact between the bolts and the rock in the roof of the mine, resin anchors have been employed which in a typical arrangement involves the insertion of resin packages into the holes which are then broken by insertion of the bolts and mixed by rotation of the bolts providing a rapid setting polymer anchor for the bolt. Fully-grouted bolts also have been used and such bolts consist of deformed bars, with or without a head, which would then be cemented into a hole using concrete or polymeric materials as grouting materials.
However, it has been found that in the application of the resin anchors as described in U.S. Pat. Nos. 3,302,410, 3,324,662 and 3,091,935, sufficient technical difficulties are involved in preparing such rockbolts that they are time consuming to prepare, expensive, and sometimes do not provide adequate physical characteristics to provide the support desired in the roof of a mine.